request error handling

source/ChromeDevTools/ChromeSession.cs

@@ -16,6 +16,7 @@ public class ChromeSession : IChromeSession
         private readonly ConcurrentDictionary<string, ConcurrentBag<Action<object>>> _handlers = new ConcurrentDictionary<string, ConcurrentBag<Action<object>>>();
         private ICommandFactory _commandFactory;
         private IEventFactory _eventFactory;
+        private readonly Action<Exception> _onError;
         private ManualResetEvent _openEvent = new ManualResetEvent(false);
         private ManualResetEvent _publishEvent = new ManualResetEvent(false);
         private ConcurrentDictionary<long, ManualResetEventSlim> _requestWaitHandles = new ConcurrentDictionary<long, ManualResetEventSlim>();
@@ -24,12 +25,13 @@ public class ChromeSession : IChromeSession
         private WebSocket _webSocket;
         private static object _Lock = new object();
 
-        public ChromeSession(string endpoint, ICommandFactory commandFactory, ICommandResponseFactory responseFactory, IEventFactory eventFactory)
+        public ChromeSession(string endpoint, ICommandFactory commandFactory, ICommandResponseFactory responseFactory, IEventFactory eventFactory, Action<Exception> onError)
         {
             _endpoint = endpoint;
             _commandFactory = commandFactory;
             _responseFactory = responseFactory;
             _eventFactory = eventFactory;
+            _onError = onError;
         }
 
         public void Dispose()
@@ -81,17 +83,17 @@ public Task<ICommandResponse> SendAsync<T>(CancellationToken cancellationToken)
             return SendCommand(command, cancellationToken);
         }
 
-        public Task<CommandResponse<T>> SendAsync<T>(ICommand<T> parameter, CancellationToken cancellationToken)
+        public Task<ICommandResponseWrapper<T>> SendAsync<T>(ICommand<T> parameter, CancellationToken cancellationToken)
         {
             var command = _commandFactory.Create(parameter);
             var task = SendCommand(command, cancellationToken);
-            return CastTaskResult<ICommandResponse, CommandResponse<T>>(task);
+            return TransformTaskResult(task, response => (ICommandResponseWrapper<T>)new CommandResponseWrapper<T>(response));
         }
 
-        private Task<TDerived> CastTaskResult<TBase, TDerived>(Task<TBase> task) where TDerived: TBase
+        private Task<TDerived> TransformTaskResult<TBase, TDerived>(Task<TBase> task, Func<TBase, TDerived> transform)
         {
             var tcs = new TaskCompletionSource<TDerived>();
-            task.ContinueWith(t => tcs.SetResult((TDerived)t.Result),
+            task.ContinueWith(t => tcs.SetResult(transform(t.Result)),
                 TaskContinuationOptions.OnlyOnRanToCompletion);
             task.ContinueWith(t => tcs.SetException(t.Exception.InnerExceptions),
                 TaskContinuationOptions.OnlyOnFaulted);
@@ -235,12 +237,12 @@ private void WebSocket_DataReceived(object sender, DataReceivedEventArgs e)
                 HandleEvent(evnt);
                 return;
             }
-            throw new Exception("Don't know what to do with response: " + e.Data);
+            _onError(new Exception("Don't know what to do with response: " + e.Data));
         }
 
         private void WebSocket_Error(object sender, SuperSocket.ClientEngine.ErrorEventArgs e)
         {
-            throw e.Exception;
+            _onError(e.Exception);
         }
 
         private void WebSocket_MessageReceived(object sender, MessageReceivedEventArgs e)
@@ -257,7 +259,7 @@ private void WebSocket_MessageReceived(object sender, MessageReceivedEventArgs e
                 HandleEvent(evnt);
                 return;
             }
-            throw new Exception("Don't know what to do with response: " + e.Message);
+            _onError(new Exception("Don't know what to do with response: " + e.Message));
         }
 
         private void WebSocket_Opened(object sender, EventArgs e)

source/ChromeDevTools/ChromeSessionExtensions.cs

@@ -5,7 +5,7 @@ namespace MasterDevs.ChromeDevTools
 {
     public static class ChromeSessionExtensions
     {
-        public static Task<CommandResponse<T>> SendAsync<T>(this IChromeSession session, ICommand<T> parameter)
+        public static Task<ICommandResponseWrapper<T>> SendAsync<T>(this IChromeSession session, ICommand<T> parameter)
         {
             return session.SendAsync(parameter, CancellationToken.None);
         }

source/ChromeDevTools/ChromeSessionFactory.cs

@@ -1,22 +1,24 @@
-#if !NETSTANDARD1_5
+using System;
+
+#if !NETSTANDARD1_5
 namespace MasterDevs.ChromeDevTools
 {
     public class ChromeSessionFactory : IChromeSessionFactory
     {
-        public IChromeSession Create(ChromeSessionInfo sessionInfo)
+        public IChromeSession Create(ChromeSessionInfo sessionInfo, Action<Exception> onError)
         {
-            return Create(sessionInfo.WebSocketDebuggerUrl);
+            return Create(sessionInfo.WebSocketDebuggerUrl, onError);
         }
 
-        public IChromeSession Create(string endpointUrl)
+        public IChromeSession Create(string endpointUrl, Action<Exception> onError)
         {
             // Sometimes binding to localhost might resolve wrong AddressFamily, force IPv4
             endpointUrl = endpointUrl.Replace("ws://localhost", "ws://127.0.0.1");
             var methodTypeMap = new MethodTypeMap();
             var commandFactory = new CommandFactory();
             var responseFactory = new CommandResponseFactory(methodTypeMap, commandFactory);
             var eventFactory = new EventFactory(methodTypeMap);
-            var session = new ChromeSession(endpointUrl, commandFactory, responseFactory, eventFactory);
+            var session = new ChromeSession(endpointUrl, commandFactory, responseFactory, eventFactory, onError);
             return session;
         }
     }

source/ChromeDevTools/CommandResponseWrapper.cs

@@ -0,0 +1,49 @@
+using System;
+
+namespace MasterDevs.ChromeDevTools
+{
+    public interface ICommandResponseWrapper<T>
+    {
+        long Id { get; }
+        string Method { get; }
+        bool IsError();
+        T Result { get; }
+        Error Error { get; }
+    }
+
+    public class CommandResponseWrapper<T> : ICommandResponseWrapper<T>
+    {
+        private readonly ICommandResponse _response;
+
+        public CommandResponseWrapper(ICommandResponse response)
+        {
+            _response = response;
+        }
+
+        public long Id => _response.Id;
+        public string Method => _response.Method;
+
+        public bool IsError() => _response is IErrorResponse;
+
+        public T Result
+        {
+            get
+            {
+                var commandResponse = _response as CommandResponse<T>;
+                if (commandResponse != null)
+                    return commandResponse.Result;
+                throw new ResultNotAvailableException((IErrorResponse)_response, typeof(T));
+            }
+        }
+
+        public Error Error => (_response as IErrorResponse)?.Error;
+    }
+
+    public class ResultNotAvailableException : Exception
+    {
+        public ResultNotAvailableException(IErrorResponse response, Type type) 
+            : base($"Unhandled command error {{ Code: {response.Error.Code}, Message: {response.Error.Message} }} to command {response.Id} requesting {type}.")
+        {
+        }
+    }
+}

source/ChromeDevTools/IChromeSession.cs

@@ -10,7 +10,7 @@ public interface ICommand<T>
     }
     public interface IChromeSession
     {
-        Task<CommandResponse<TResponse>> SendAsync<TResponse>(ICommand<TResponse> parameter, CancellationToken cancellationToken);
+        Task<ICommandResponseWrapper<TResponse>> SendAsync<TResponse>(ICommand<TResponse> parameter, CancellationToken cancellationToken);
 
         Task<ICommandResponse> SendAsync<T>(CancellationToken cancellationToken);
 

source/ChromeDevTools/IChromeSessionFactory.cs

@@ -1,7 +1,9 @@
-namespace MasterDevs.ChromeDevTools
+using System;
+
+namespace MasterDevs.ChromeDevTools
 {
     public interface IChromeSessionFactory
     {
-        IChromeSession Create(string endpointUrl);
+        IChromeSession Create(string endpointUrl, Action<Exception> onError);
     }
 }

source/ChromeDevTools/MasterDevs.ChromeDevTools.csproj

@@ -60,6 +60,7 @@
   </ItemGroup>
   <ItemGroup>
     <Compile Include="ChromeProcessFactory.cs" />
+    <Compile Include="CommandResponseWrapper.cs" />
     <Compile Include="IDirectoryCleaner.cs" />
     <Compile Include="LocalChromeProcess.cs" />
     <Compile Include="ChromeSession.cs" />

source/Sample/Program.cs

@@ -16,82 +16,99 @@ private static void Main(string[] args)
         {
             Task.Run(async () =>
             {
-                // synchronization
-                var screenshotDone = new ManualResetEventSlim();
-
                 // STEP 1 - Run Chrome
                 var chromeProcessFactory = new ChromeProcessFactory(new StubbornDirectoryCleaner());
                 using (var chromeProcess = chromeProcessFactory.Create(9222, true))
                 {
-                    // STEP 2 - Create a debugging session
-                    var sessionInfo = (await chromeProcess.GetSessionInfo()).LastOrDefault();
-                    var chromeSessionFactory = new ChromeSessionFactory();
-                    var chromeSession = chromeSessionFactory.Create(sessionInfo.WebSocketDebuggerUrl);
-
-                    // STEP 3 - Send a command
+                    // STEP 2 - Handle communication errors
                     //
-                    // Here we are sending a commands to tell chrome to set the viewport size 
-                    // and navigate to the specified URL
-                    await chromeSession.SendAsync(new SetDeviceMetricsOverrideCommand
+                    // There are two ways how to handle communication errors:
+                    // 1) check .IsError() for every command before accessing the .Result
+                    // 2) access the .Result directly and handle (or don't handle ..) the exception
+                    // We are using here the second option
+                    try
                     {
-                        Width = ViewPortWidth,
-                        Height = ViewPortHeight,
-                        Scale = 1
-                    });
+                        // STEP 3 - Create a debugging session
+                        var sessionInfo = (await chromeProcess.GetSessionInfo()).LastOrDefault();
+                        var chromeSessionFactory = new ChromeSessionFactory();
+                        var chromeSession = chromeSessionFactory.Create(sessionInfo.WebSocketDebuggerUrl,OnError );
 
-                    var navigateResponse = await chromeSession.SendAsync(new NavigateCommand
-                    {
-                        Url = "http://www.google.com"
-                    });
-                    Console.WriteLine("NavigateResponse: " + navigateResponse.Id);
-
-                    // STEP 4 - Register for events (in this case, "Page" domain events)
-                    // send an command to tell chrome to send us all Page events
-                    // but we only subscribe to certain events in this session
-                    var pageEnableResult = await chromeSession.SendAsync<Protocol.Chrome.Page.EnableCommand>();
-                    Console.WriteLine("PageEnable: " + pageEnableResult.Id);
+                        // STEP 4 - Send a command
+                        //
+                        // Here we are sending a commands to tell chrome to set the viewport size 
+                        // and navigate to the specified URL
+                        await chromeSession.SendAsync(new SetDeviceMetricsOverrideCommand
+                        {
+                            Width = ViewPortWidth,
+                            Height = ViewPortHeight,
+                            Scale = 1
+                        });
 
-                    chromeSession.Subscribe<LoadEventFiredEvent>(loadEventFired =>
-                    {
-                        // we cannot block in event handler, hence the task
-                        Task.Run(async () =>
+                        var navigateResponse = await chromeSession.SendAsync(new NavigateCommand
                         {
-                            Console.WriteLine("LoadEventFiredEvent: " + loadEventFired.Timestamp);
+                            Url = "http://www.google.com"
+                        });
+                        Console.WriteLine($"NavigateResponse: {navigateResponse.Id}");
 
-                            var documentNodeId = (await chromeSession.SendAsync(new GetDocumentCommand())).Result.Root.NodeId;
-                            var bodyNodeId =
-                                (await chromeSession.SendAsync(new QuerySelectorCommand
-                                {
-                                    NodeId = documentNodeId,
-                                    Selector = "body"
-                                })).Result.NodeId;
-                            var height = (await chromeSession.SendAsync(new GetBoxModelCommand {NodeId = bodyNodeId})).Result.Model.Height;
+                        // STEP 5 - Register for events (in this case, "Page" domain events)
+                        //
+                        // send an command to tell chrome to send us all Page events
+                        // but we only subscribe to certain events in this session
+                        var pageEnableResult = await chromeSession.SendAsync<Protocol.Chrome.Page.EnableCommand>();
+                        Console.WriteLine($"PageEnable: {pageEnableResult.Id}");
 
-                            await chromeSession.SendAsync(new SetDeviceMetricsOverrideCommand
-                            {
-                                Width = ViewPortWidth,
-                                Height = height,
-                                Scale = 1
-                            });
+                        // We cannot do other requests in event handler, therefore we only wait for the event to be triggered
+                        // and continue in the main program flow
+                        var loadEventFired = new ManualResetEventSlim();
+                        chromeSession.Subscribe<LoadEventFiredEvent>(ev =>
+                        {
+                            Console.WriteLine($"LoadEventFiredEvent: {ev.Timestamp}");
+                            loadEventFired.Set();
+                        });
+                        loadEventFired.Wait();
 
-                            Console.WriteLine("Taking screenshot");
-                            var screenshot = await chromeSession.SendAsync(new CaptureScreenshotCommand {Format = "png"});
+                        // The page is ready in the browser, now we can take the screenshot
 
-                            var data = Convert.FromBase64String(screenshot.Result.Data);
-                            File.WriteAllBytes("output.png", data);
-                            Console.WriteLine("Screenshot stored");
+                        // update the VisibleSize to include whole page (extending height)
+                        var documentNodeId = (await chromeSession.SendAsync(new GetDocumentCommand()))
+                            .Result.Root.NodeId;
+                        var bodyNodeId =
+                        (await chromeSession.SendAsync(new QuerySelectorCommand
+                        {
+                            NodeId = documentNodeId,
+                            Selector = "body"
+                        })).Result.NodeId;
+                        var height = (await chromeSession.SendAsync(new GetBoxModelCommand {NodeId = bodyNodeId}))
+                            .Result.Model.Height;
 
-                            // tell the main thread we are done
-                            screenshotDone.Set();
+                        await chromeSession.SendAsync(new SetDeviceMetricsOverrideCommand
+                        {
+                            Width = ViewPortWidth,
+                            Height = height,
+                            Scale = 1
                         });
-                    });
 
-                    // wait for screenshoting thread to (start and) finish
-                    screenshotDone.Wait();
+                        Console.WriteLine("Taking screenshot");
+                        var screenshot = await chromeSession.SendAsync(new CaptureScreenshotCommand {Format = "png"});
+
+                        var data = Convert.FromBase64String(screenshot.Result.Data);
+                        File.WriteAllBytes("output.png", data);
+                        Console.WriteLine("Screenshot stored");
+                    }
+                    catch (ResultNotAvailableException ex)
+                    {
+                        Console.WriteLine($"Error while taking screenshot: {ex.Message}");
+                    }
 
                     Console.WriteLine("Exiting ..");
                 }
             }).Wait();
         }
+
+        private static void OnError(Exception exception)
+        {
+            Console.WriteLine("Error during communication:");
+            Console.WriteLine(exception);
+        }
     }
 }